Acoustic apparatus called speakers usually transmit sound by converting electrical sound signals output from an amplifier or the like to sound vibrations by the use of electromagnetic or electrostatic stress, transmitting the sound vibrations to a vibrating board consisting of a cone paper etc., and vibrating air between the vibrating board and a listener's eardrums properly.
Such speakers are ranging for large business concerns, including products for generating loud sounds used by musicians at open-air concerts, household stereos, minicomponents, radio cassette recorders, and headphones. 5.1 channel speakers were also developed and have recently been spreading as household stereos.
FIG. 11 is a horizontal cross-sectional view of a conventional household stereo speaker.
In a conventional speaker system, two speaker units 21, 22 with a speaker box 23 or 24 are employed. The speaker box 23, 24 is required since the speaker unit 21, 22 itself cannot reproduce a sound in a low sound range. The speaker box 23, 24 consists of a resonance box with an appropriate volume obtained by a predetermined calculation. Now, descriptions of the speaker box 23 will be given. The same applies to the speaker box 24. A fitting hole corresponding to the size of the speaker unit 21 is made in a baffle board 25, which forms a front board. The speaker unit 21 is fitted into the hole airtightly so that a vibrating board consisting of a cone paper 27 of the speaker unit 21 blocks the hole. This prevents air from flowing from the inside of the baffle board 25 to the outside of the baffle board 25 and vice versa. The speaker unit 21 is fixed firmly onto the baffle board 25 by inserting, for example, wood screws (not shown) from the front into tapped holes (not shown) in a frame of the speaker unit 21 and tightening them.
The primary object of the baffle board 25 is to isolate a sound wave which is generated in front of the cone paper 27 from a sound wave which is generated behind the cone paper 27 and to prevent them from interfering with each other. In this case, sound waves with phases opposite to each other will be generated. Mixing sound waves with phases opposite to each other, that is to say, a sound wave 5 and a sound wave 5′ will result in zero. That is to say, a sound which is generated by the speaker unit 21 will vanish before it can reach a listener's ears 29 and 30.
The wavelength of a sound wave especially at a low compass is long. Even if the listener's ears 29 and 30 are rather far from the speaker unit 21, a shift in the phase of a sound wave is slight. Therefore, the above cancel relationship between two sound waves with phases opposite to each other always exists. Theoretically, the baffle board 25 must consist of a board of infinitely great size so that it can prevent air from flowing from the inside of the baffle board 25 to the outside of the baffle board 25 and vice versa. Moreover, the baffle board 25 itself should be heavy and strong and should not vibrate. Furthermore, the baffle board 25 should be fixed firmly.
When the cone paper 27 moves forward by the electromagnetic driving force of a voice coil (not shown), a high air-density portion (hereinafter referred to as a “positive” for convenience of explanation) appears in front of the cone paper 27 and a low air-density portion (hereinafter referred to as a “negative” for convenience of explanation) appears behind the cone paper 27. On the other hand, when the cone paper 27 moves backward, a low air-density portion (negative) appears in front of the cone paper 27 and a high air-density portion (positive) appears behind the cone paper 27. Isolating the positive from the negative will prevent a sound at a low compass from attenuating.
In this case, “the action of isolating the sound wave 5′ (6′) with a phase opposite to that of the sound wave 5 (6) generated behind the cone paper 27 (28) from the sound wave 5 (6)” has a great effect. This is called a first operating principle.
There is another type of speaker in which a negative, which appears behind the cone paper 27 when a sound wave moves forward, is converted to a positive in a cylindrical portion (not shown) in the speaker box 23, the positive is radiated from a predetermined hole (not shown) in the baffle board 25, and the cone paper 27 adds force to the positive. Its operating principle is the same with a passive radiator described later with reference to FIG. 12.
In a word, sound waves may cancel out each other by subtraction or may increase their intensity by addition. Therefore, in order to make a speaker, which can reproduce a sound with high fidelity at a predetermined level, it is necessary to design a speaker box or an enclosure, in consideration of the frequency and phase of waves which interfere with each other.
The speaker box 23 usually resonates only the air inside. That is to say, the enclosure member etc. of its resonance box, including the baffle board 25, do not vibrate or resonate. The speaker box 23 is therefore heavy and strong. A wadding-like sound absorbing material 31 is attached to its inner wall. The sound absorbing material 31 absorbs the sound wave 5′. That is to say, the sound absorbing material 31 absorbs harmful waves generated, for example, a sound reflected by the inner wall of the resonance box.
However, such a sealed box does not always achieve theoretically perfect high fidelity sounds so as to be recognized as a standard type as a structure around a speaker unit, because the sound absorbing material 31 could not absorb all the sound waves and slight harmful interference waves remain, and the damper effect due to the closed air within the sealed box restricts a free vibration of the cone paper.
If the enclosure member itself vibrates unnecessarily, then a harsh noise will be produced. Furthermore, if an LP record player is located near the speaker and sounds reproduced by the LP record player is used as a source, a howl may be produced. Therefore, a desired clear sound has been produced by eliminating unnecessary vibrations to the utmost.
This can be said to a frame 15, which supports the cone paper 27 in a vibration-free manner. In other words, the frame 15 is fixed firmly onto the baffle board 25 so that the frame 15 itself does not vibrate.
The well-known fact that “a large, heavy, and strong enclosure etc. for an acoustic apparatus, such as a speaker, which do not vibrate, will produce a clear sound” is based on:                (1) the object of desiring comfortable resonance at a low compass,        (2) the object of avoiding the harm of waves with phases opposite to each other canceling out each other, that is to say, the harm of sound failing, and        (3) the reason that harm caused by a harsh noise should be avoided.        
On the basis of these objects and reason, in a speaker equipped with a resonance boxe consisting of a sealed box etc., a forward and backward movement of the cone paper is limited by air pressure. As a result, a strange sound is produced.
A listener catches not only direct sounds from the cone papers 27 and 28, viz. the L-channel sound wave 5 and the R-channel sound wave 6 but also reverberations produced by an inner wall 32, a floor 33, and a ceiling 34 of a listening room. This is an ordinary listening method.
In this case, even if the same speaker system is used, timbre will vary with the fixtures of the listening room, the location of a listener, or his/her posture. This is a well-known fact.
Unlike the above listening method using a conventional speaker system comprising the speaker boxes 23 and 24, only direct sounds can be transmitted by the use of headphones (not shown). With this method, the distance between the vibrating boards of miniature speakers (not shown) and a listener's eardrums (not shown) is shortened.
In this case, since reverberations do not exist, their comfortable reverberation does not exist. However, there are no waves exit which harmful to the original sound. As a result, the original sound can always be reproduced with high fidelity. If a listener puts on the headphones, timbre will not vary with the fixtures of the listening room, his/her location, or his/her posture. This is well-known and natural. Only temperature, atmospheric pressure, and humidity around a listener's ears may have an influence on the above direct sounds and the influence on the timbre is slight in an ordinary atmosphere.
If members etc. of the headphones used in the second listening method vibrate unnecessarily, a harsh noise will be produced. This is the same with a case where unnecessary vibrations occur in the speaker boxes 23 and 24. Therefore, a clear sound has been reproduced with high fidelity by eliminating unnecessary vibrations to the utmost.
Therefore, the frames etc. (not shown) of the miniature speakers are joined firmly to members etc. (not shown) of the headphones with, for example, an adhesive so that the members etc. of the headphones do not vibrate unnecessarily.
Furthermore, a special speaker system known from the trademark of Body sonic has been used with an easy chair. The speakers have a very relaxing effect on a person by transmitting non-audio ultra-low frequency vibrations directly to the human body not via air but via a member of, for example, the easy chair (not shown). In this case, vibrations are also transmitted to a part of the members and to its cushion portion. This is a conventional example indicating the application of a speaker.
Moreover, unlike conventional speakers having strong enclosures, there are special speakers (not shown) which vibrate their members themselves. These special speakers do not have ordinary cone papers as vibrating portions in their speaker units. Instead, vibration generating portions in their speaker units themselves are fitted directly on design panels or wall boards not via frames etc. and the design panels or wall boards vibrate. As a result, sound is emitted from the design panels or wall boards themselves. This is also a special example in which vibration is transmitted to a member, and a conventional example indicating, for example, a method for fixing speaker units to members.
In the above speakers, regardless of their types, speaker units and fitting portions to which they are fixed are joined reliably with wood screws or an adhesive in order to avoid noise produced by the above unnecessary vibrations.
As stated above, most conventional speakers have resonance boxes to output reproduced sounds efficiently. With those speakers, in order to prevent sound waves with phases opposite to each other generated in front of and behind cone papers from canceling out each other, spaces in front of the cone papers are isolated from spaces behind the cone papers. Furthermore, resonance brings about high and efficient sound output.
With a speaker shown in FIG. 12, however, a “passive-radiation type freely-vibrating board without a driving voice coil 92 etc.” (hereinafter referred to as a “passive radiator”) 82 and a cone paper 27 of a speaker unit 91 are located on one baffle board.
With this speaker, the driving force of the voice coil 92 causes the cone paper 27 to move forward and backward. As a result, a positive sound wave 5 is generated in front of the cone paper 27 and a negative sound wave 5′ is generated behind the cone paper 27. This is the same with a sealed resonance box. The negative sound wave 5′ is converted to a positive sound wave by the interference action of a partition board 93 and presses the passive radiator 82 forward. A positive sound wave 50 therefore is generated. As a result, there is the effect of strengthening the sound waves 5 and 50 at a particular frequency.
In this case, “the action of radiating resonating sounds” has a great effect. This is called a second operating principle.
While there is the effect of strengthening sound waves at a particular frequency, there is no denying its unnaturalness.
The most conventional type of speaker is a large-sized stationary speaker consisting of two or more heavy and strong enclosures. These enclosures are independent of one another. If there are two enclosures, one is used only for L-channel sound and the other is used only for R-channel sound. Without a device, it will be difficult for the other types of speaker store produce the original sound with high fidelity and to reproduce heavy low-pitched sounds with presence.
Headphones are well-known as means for listeners to easily and reliably reproduce powerful heavy low-pitched sounds with a stereophonic effect peculiar to a stereo. However, many people dislike them because of their uncomfortableness or obstacle cords.
Therefore, headphones are practicable for business purposes, but they are impracticable for relaxing purposes.
With most headphones, an ear and a speaker unit applied to it are covered together with, for example, a rigid cover with a cushion in order to shut off the ear from sound which comes from the other channel and the outside. Therefore, even when a speaker unit and an ear are a short distance away, sound which comes from the speaker unit will be very faint.
With open headphones, sound which comes from a speaker unit will also be faint when it is moved a short distance from the normal position.
With a compact stereo for, for example, a radio cassette recorder or a television which can receive voice multiplexed stereo broadcasting, a configuration in which one of two speaker units outputs only L-channel sound and the other outputs only R-channel sound maybe adopted. In this case, these two speaker units are located at both ends of one lightweight plastic enclosure (not shown). As a result, L-channel sound waves interfere with R-channel sound waves via the lightweight enclosure. Moreover, the distance between the two speaker units is short, so the L-channel and R-channel sound waves will mix in the air before they reach a listener's ears. That is to say, even if a stereo is used, the listener cannot enjoy its stereophonic effect.
In order to address such problems, the present invention was made. In other words, an object of the present invention is to provide powerful high-fidelity heavy low-pitched sounds and a stereophonic effect, which could obtain only by high-quality headphones or a large-sized speaker, to a listener.
It is preferable that the attenuation of sound should be minimized even in a listening room the sound absorbing structure of which is not desirable in terms of sound effects.
It is preferable that a speaker with the same performance as a conventional one should be priced down.
It is preferable that clear agreeable sounds which relax a listener should be reproduced.
A speaker without a resonance box will be able to meet the above conditions.
Furthermore, it is preferable that a licensee who uses the present invention should be able to realize the most effective results reliably without using the method of trial and error.
It is preferable that material used should be minimized by making effective use of the function of aback sound screening board.
It is preferable that, by adapting an accordion wall or the like for partitioning a room, it should serve not only as a fitting but also as a back sound screening board.
Another object of the present invention is to provide a speaker used in a pillow, being a piece of bedding, or the pillow portion of an easy chair for listening to, for example, music.
Still another object of the present invention is to provide a miniature, lightweight, and low-cost speaker which can reproduce clear sounds not only to conventional audio and video apparatus but also to electric and electronic apparatus for which importance has not been attached to tone quality.